Multi fluid injection mixer

ABSTRACT

This disclosure includes mixers and methods of mixing. Some mixers comprise at least one contacting element, each defining at least one mixing channel. Each of the mixing channel(s) can have a cross-sectional area that decreases in a downstream direction to accelerate any pipe fluid flowing through the mixing channel. The contacting surface of each of the mixing channel(s) can deflect at least a portion of any pipe fluid flowing through the mixing channel until the contacting surface ends at an edge at a point of maximum constriction. Each of the contacting element(s) can define one or more injection path(s) to at least one of the contacting surface(s), each configured to inject admixture fluid onto the contacting surface such that the admixture fluid is entrained by pipe fluid over the edge.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/664,382 filed Apr. 9, 2009, which is a national phase applicationunder 35 U.S.C. § 371 of International Application No.PCT/N02005/000352, filed Sep. 23, 2005, which claims priority toNorwegian Application No. 20044181, filed Oct. 1, 2004, and NorwegianApplication No. 20044854 filed Nov. 8, 2004. The entire text of each ofthe above-referenced disclosures is specifically incorporated herein byreference without disclaimer.

FIELD OF THE INVENTION

The present invention relates to injection into, mixing and conditioningof fluids flowing through a pipeline. More particularly the inventionrelates to a multi fluid injection mixer, a mixer and an assemblyincluding the multi fluid injection mixer, feasible for a large numberof mixing, injection and conditioning operations, particularly relatedto processing hydrocarbons and in-line reactor processes for theproduction of fine chemicals.

BACKGROUND OF THE INVENTION AND OR ART

Processing of fluids is a large technical field finding applications inmost industries. Processing of fluids flowing in a pipeline typicallyinvolves phase separation of the fluid contents and delivery of theseparated constituents at a specified quality, according to subsequentuse. For example the stream from a hydrocarbon well is separated intooil, gas and water, the phases being processed and cleaned forcontaminants until a specification is met. The processing will typicallyinvolve injection of fluids such as chemicals, solvents or extractionfluids for enhancing the effect of the separation and processingequipment.

The most commonly injected fluids (admixtures) can be summarized asfollows:

Scavengers/irreversible solvents (liquid for removal of sourconstituents, such as eg. H₂S, Mercury, Mercaptans)

Corrosion inhibitors, Hydrate inhibitors, Scale inhibitors, Waxinhibitors

Drag reducers, Desalters, De-emulsifiers, Deoilers, Defoamers,

Antifoulants

Flocculants (enhancing the coalescence rate of the dispersed phase)

Condensate/hydrocarbon (extraction fluids)

Gas (flotation or alleviation of slugging)

Water (desalting or manipulation of the water cut of a multiphase flowmixture away from its critical value)

The respective admixture fluids are typically introduced into the flowof a pipe upstream of processing equipment, such as upstream of aseparator. The flow can be any multiphase mixture of gas and one or moreliquids, a single gas or a combination of gases, any liquid or mixtureof miscible liquid components or immiscible components such ashydrocarbon liquid and water. Hence, the flow can be for exampleunprocessed well stream, produced water, processed oil-water flow,processed gas flow, produced water contaminated with dispersed anddissolved hydrocarbon, processed water flow contaminated withhydrocarbon liquid, or water subject to gas component removal (e.g.de-oxygenation). The range of surface tension, viscosity, pressure andtemperature may vary considerably, and additional types of fluids oradmixtures are also relevant.

Whereas the description above and below mainly relates to processing ofhydrocarbons, the mixing of fluids is an essential unit operation alsoin other parts of the process industry, such as production of food (e.g.production of emulsion), pharmaceuticals, chemicals (reactive flow whichmay involve activators or reagents), paper (refining/treatment of pulp),melts (alloys) and other processes. These processes in general involvebatch production using large vessels, where the different fluids aremixed by means of agitators. It is reason to believe that using pipeflow mixing instead of agitation in vessels is attractive both due toinvestment, operational costs, flexibility in production, safety andproduct quality.

Typically, the flow rate of the admixture injected into the pipe isextremely small as compared to the volumetric flow rate of for example amultiphase flow. The challenges with the feed of the admixture aretherefore associated with obtaining a steady non-oscillating injectionrate, safeguarding axial mixing and simultaneously achieving homogeneousdispersion and distribution of the admixture over the pipe cross-sectionof the multiphase flow in concern (radial mixing).

The resulting droplet size distribution of the dispersed injectedadmixture is affected by the mixer design, fluid properties and flowrates in concern.

Injection quills are the most common injection device for admixtures,but injection quills provide no effective distribution of the chemicalinto the multiphase flow. With requirement to achieve steady-stateinjection rate, also the turn-down in the flow rate of the admixture islimited. Nozzles normally provide better distribution than quills of theinjected fluid into the continuous phase. Disadvantages are howeverassociated with limitations in secondary break-up of droplets, narrowoperational range of flow rate of the admixture (turn-down) and limitedmechanical robustness. Also the scale-up towards higher pipe dimensionsis questionable.

For the Sulzer mixer and similar static mixers the admixture is injectedupstream of the mixer. The mixers are based on plates or bafflesinstalled in series such that the multiphase flow is repeatedly exposedtowards high shear forces in order to finally gain an acceptable mixtureof the injected fluid and the continuous fluid phase. Typically thisrequires a considerable pressure drop (equivalent to high energyconsumption, limitation in capacity or production rate) and long mixerinstallation units. Such mixers typically yield a fairly non-uniformdroplet distribution of the injected admixture for practical lengths ofthe static mixers as only a part of the admixture is exposed to the highshear forces at the surface of the baffles or plates.

One-shot mixers such as chokes or venturies expose the inflowingmultiphase flow towards a zone of high shear accomplished within afairly short mixer. As for these mixers the injected fluid ispre-injected upstream of the mixer device, the injected fluid isentrained with the bulk of the continuous phase. Accordingly theinjected fluid is in general not exposed to the part of the mixer wherethe shear forces are high; the vicinity of the mixer wall. In order tocompensate for this and secure the break-up of the injected fluid (asassociated with stretching of “fluid elements” in regions of high shear;large gradient in fluid velocity), a high pressure drop over the mixerneeds to be imposed.

The Westfall Manufacturing Company of Bristol, R.I., USA offers a staticmixer which is adapted for disposition in a pipe containing fluid flow,the static mixer including a circumferential flange radially inwardlyextending from the internal pipe surface and in turn having at least apair of opposed flaps extending there from and inclined in the directionof the fluid flow. Said static mixer is described in patent publicationU.S. Pat. No. 5,839,828, to which document reference is made. Operationof the static mixer results in a combination of laminar and turbulentflow column 1, line 36-39). Further, chemicals can be added throughinjection ports on the downstream side of the flaps (claim 4, FIGS. 10and 7, column 3 line 21-33 and 59-62). In this device the chemical ispoint injected behind a plate, namely a flap, and not injected such thatthe chemical is homogeneously distributed in the continuous phase. Thereis no description of any sharp edge.

By the invention of the ProPure injection mixer designated C100, asdescribed in patent application EP 01947618.3, the technology for mixingand injection was advanced. The injection mixer C100 consists of acontacting element formed as a contracting pipe through which a gasstream flows, and an injection element consisting of a liquid inletconfigured to produce an annulus of liquid around the internal perimeterof the contracting pipe, a sharp edge at the end of the contracting pipeand a further pipe section downstream of the sharp edge. Preferably thedownstream pipe section is a diverging pipe to recover some of thepressure dropped over the contracting section. In patent application EP01947618.3 it is described how the injection mixer C100 can be used fordistributing a liquid into a gas stream, for absorbing a selected gascomponent from a gas stream by bringing the gas stream into contact witha liquid including a solvent or a reagent for the selected gascomponent, for scavenging H₂S from natural gas, for selectively removingH₂S from a natural gas in preference to CO₂, for simultaneously removingacid gas components from a natural gas stream, for deoxygenizing water,for dehydrating natural gas, and how it is used in combination withexisting columns to adapt an existing plant to accommodate a change inthe feed conditions. Additionally it is described how the injectionmixer can be used as a mixer for remixing the phases in a fluid flow,without injection of chemicals. It is also described how severalinjection mixers can be combined in series or in parallel to injectseveral liquids, by injecting one chemical in each mixer (cf. claims 15,16, FIGS. 10a and 10b of EP 01947618.3). Injection of several admixturefluids in one injection mixer is not considered in EP 01947618.3,probably because injection of several admixture fluids simultaneously isconsidered inefficient. For example, injection of a gas together with aviscous liquid is considered inefficient since the admixture fluids arenot expected to mix intimately because of the large difference in fluidproperties as density, surface tension and viscosity. This, combinedwith flow rate in concern and resulting pressure gradient over theinjection conduit in concern, may serve to cause oscillating injectionflow rates for at least one of the injected admixture fluids. Based onthe teaching of EP 01947618.3 the person of ordinary skill in the artwill only consider injection of liquid into a gas flow, only oneinjection element will be considered and only a contacting elementformed as a contracting pipe will be considered, as there is noindications of different embodiments or the possibilities for improvedtechnical effect.

Despite the advantageous properties of the C100 injection mixer, ademand exists for technology simplifying injection several chemicals oradmixtures with one injection mixer, thus reducing the pressure drop andthe number of injection mixers. A demand also exists for improvedtechnical effect over the C100 injection mixer with respect to mixing ofthe admixture fluid, particularly with multi fluid injection, depositionof the admixture on the internal pipe wall, and also alternativeconstructions of an injection mixer, which can prove to be advantageousfor specific applications, such as modifying existing equipment toimprove the technical effect. A demand exists for an injection mixerwith a steady, non-oscillating, minimized admixture injection rate(axial mixing) and homogeneous dispersion and distribution of thechemical into the fluid phases (radial mixing), over a wide range offlow conditions, with a narrow range of droplet/bubble sizes, at lowpressure drop and low admixture deposition rate. A demand also existsfor a mixer for homogenously mixing of fluids flowing in a pipe. Afurther demand exists for an assembly of an injection mixer withadditional equipment, particularly feasible for treatment of producedwater, treatment of oil, desalting and flow assurance.

SUMMARY OF THE INVENTION

The above-mentioned demands are met with the present invention, byproviding a multi fluid injection mixer for injecting gas and/or liquidas admixture fluid to gas and/or liquid flowing through a pipe, andhomogeneously mixing the admixture fluids and pipe fluids, saidinjection mixer constituting a section of the pipe.

The multi fluid injection mixer is distinguished by comprising:

at least one contacting element having at least one contacting surfacefacing and deflecting some of the pipe fluid flow, forming aconstriction to the internal cross-section of the pipe, such that thepipe fluid flow is accelerated and fluid flowing in the vicinity of saidsurface is deflected to flow along the surface until the surface endover a sharp edge at the point of maximum constriction and flowvelocity,

at least one injection element arranged with a fluid connection to saidsurface of the contacting element, such that admixture fluid can beinjected onto said surface and along said surface be entrained by theflowing pipe fluid over the sharp edge, but for a contacting elementformed as a contracting pipe section at least two injection elements areprovided.

Preferably the contacting element is formed as a coaxial to the pipeaxis located inverse cone, as this provides a favorable technicaleffect, particularly with respect to deposition of admixture fluid onthe internal pipe surface. An inverse cone formed contacting element hasthe sharp edge at the base of the cone, i.e. the widest part of thecone. A cone section formed contacting element has the sharp edge at thenarrow base of the cone, i.e. the narrow or crusted part of the cone.

Preferably the contacting element comprises several cone sections,arranged over the cross section of the pipe, for example 7 conesections, which results in increased sharp edge length relative to thecross section of the pipe, and thereby a favorable technical effect,particularly for larger pipe dimensions. Similarly the contactingelement may favorably comprise several inverse cones or inverse conesections, arranged over the cross section of the pipe, for exampleside-by-side.

Preferably the contacting element is formed as one or several inversecone cross-section rings, which means at least one ring-formedcontacting element where a cross section along the radius is formed asan inverse cone with two deflecting surfaces. Further, the contactingelement may comprise combinations of the above mentioned embodiments,such as one coaxial to the pipe axis located inverse cone and at leastone inverse cone cross-section ring.

Preferably at least one passageway for pipe fluid flow along theinternal pipe wall, bypassing the contacting element, is provided, whichresults in pipe fluid flow along the internal pipe wall reducing theadmixture deposition on the internal pipe wall.

Preferably the contacting element is assembled from interchangeableparts, allowing for adaptation of the form of the contacting element tothe prevailing conditions, preferably adaptable such that homogenousmixing is achievable over the full pipe cross section at any relevantcondition of flow. Further, the contacting element preferably includes asuspension having spring action, such that increased pipe flow rateresults in increased opening for admixture and flow rate of admixture,thus providing a self regulating injection rate of admixture. Thecontacting element and the injection element are preferably integratedas one unit.

Preferably the injection element comprises a channel or apertures forinjecting admixture fluid evenly over the deflecting surface of thecontacting element, upstream of the sharp edge, one injection element ispreferably arranged for each intended admixture fluid, and injectionelements for gases are preferably arranged upstream of injectionelements for liquids. Further, the injection elements are preferablyadjustable with respect to apertures and pressure for flow rate ofadmixture fluid of any type or mixture of admixture fluids.

Diverging pipe sections or elements are preferably arranged downstreamof contacting element, to provide a controlled volume of turbulence andapproach to the pipe pressure and flow velocity, by bringing the flowcross section gradually back to the pipe cross section. However, thetechnical effect is favorable also when connecting the multi fluidinjection mixer directly to the downstream pipe or connection. Hence, adiverging pipe or a similar element is not obligatory, which issurprising in view of patent application EP 01947618.3.

The invention also provides a mixer for homogenous mixing of fluidsflowing through a pipe, said mixer constituting a section of the pipe,distinguished in that the mixer is comprising:

at least one contacting element having at least one surface facing anddeflecting some of the pipe fluid flow, forming a constriction to theinternal cross-section of the pipe, such that the pipe fluid flow isaccelerated and fluid flowing in the vicinity of said surface isdeflected to flow along the surface until the surface end over a sharpedge at the point of maximum constriction and flow velocity. The mixerpreferably includes at least one of the features mentioned aboverelating to the contacting element.

The invention also provides an assembly, distinguished in that it iscomprising a multi fluid injection mixer according to the invention, apipe section connected in a first end to the outlet of the injectionmixer and a re-mixer according to U.S. Pat. No. 5,971,604, connected toa second end of the pipe.

With the phrase the injection mixer constituting a section of the pipeit is meant that the injection mixer is inserted as a section in thepipe, or inserted at the beginning or end of the pipe, such that thepipe fluids flow through the injection mixer. The term homogenouslymixing means in this context intimately mixing, preferably over the fullcross section of the pipe, with the admixture fluids uniformlydistributed as droplets or bubbles of very small size, typically of asize measured in microns. The term a sharp edge means in this context aslip edge where the injected fluids slip from the internal surface,breaking up into filaments. Subsequently the filaments are broken upinto small droplets or bubbles. The sharp edge will usually form anacute angle. The phrase that the sharp edge is located at the point ofmaximum constriction and flow velocity, implies that the sharp edge isat the downstream and most constricted end of the internal surface,related to the flow direction along the internal surface, and that thecross section for the fluid flow immediately further downstream of thesharp edge is somewhat expanded. A stagnant volume is thus formedleeward of the sharp edge, which stagnant volume is essential forcreating a section of intense turbulence considered crucial forhomogenously mixing of the admixture fluids and pipe fluids.

Surprisingly it is now possible to inject more than one admixture fluidof any type in one single injection mixer, with one ore more injectionelements, even if one admixture fluid is a very viscous liquid andanother admixture fluid is a gas. Surprisingly the technical effect canbe achieved also with other forms of the contacting element than acontracting pipe, and some embodiments provide a significant improvementof the technical effect, while other embodiments may open up formodifications of existing equipment to improve the technical effect.

In its simplest embodiment the multi fluid injection mixer of theinvention can comprise one baffle plate or a flap, including oneinjection element with point injection of admixture fluid onto theinternal surface of the baffle plate or flap, which embodiment undermany conditions can be preferable to prior art injection mixers.

The contacting element is most preferably formed as one or more inversecones or inverse cone cross-section rings, which is considered mostpreferable to achieve homogenous mixing over the full pipe crosssection, with the lowest flow rate of admixture fluids, over the widestrange of prevailing conditions and lowest deposition rate. Preferablythe stagnant zones leeward of sharp slip edges do not extend to theinternal pipe wall for the full pipe circumference, most preferably theydo not extend to the internal pipe wall at all, as this reduces thedeposition rate. To this end, the contacting element deflects the pipeflow away from the internal pipe wall over a part of the pipecircumference at maximum.

Alternatively the contacting element is formed as a plate with at leastone opening, as a gutter ring, or as one or more baffle plates or flaps.The embodiment of the contacting element formed as a baffle plateincludes modifications of prior art mixers with injection elementsincorporated, for example Sulzer mixers with at least one injectionelement included in at least one baffle plate, or a choke with aninjection element included in the choking surface, or the Westfallstatic mixer with injection onto at least one flap.

One injection element is preferably arranged for each intended admixturefluid, on each contacting element, and injection elements for gases arepreferably arranged upstream of injection elements for liquids, as thishas proved to be effective. Miscible admixture fluids can be injectedthrough one injection element. Admixture fluids forming the more stablefilm flow, usually the more viscous admixtures, are in general injectedcloser to the sharp edge than admixture fluids forming less stablefilaments or films.

The invention also provides a mixer for homogeneously mixing of fluidsflowing through a pipe, said mixer constituting a section of the pipe,said mixer being identical to the injection mixer except that theinjection elements are omitted.

An assembly is also provided by the invention, distinguished in that itis comprising an injection mixer according to the present invention, apipe section connected in a first end to the outlet of the injectionmixer and a re-mixer in accordance to patent U.S. Pat. No. 5,971,604,connected to a second end of the pipe.

DRAWINGS

The present invention is illustrated with drawings, of which:

FIG. 1 is a cross-section along the longitudinal axis of a multi fluidinjection mixer according to the present invention, namely an inversecone ring mixer,

FIG. 2 is a view from below of the mixer of FIG. 1,

FIG. 3 is a multi fluid injection mixer according to the presentinvention, having 7 cone formed contacting elements,

FIG. 4 is a multi fluid injection mixer according to the presentinvention, where the contacting element is formed as an inverse cone,

FIG. 5 is an inverse cone ring mixer according to the present invention,and

FIG. 6 illustrates an assembly according to the present invention.

FIG. 7 and FIG. 8 show some typical parameters where three embodimentsof the invention are compared with the C100 mixer.

DETAILED DESCRIPTION

Reference is first made to FIG. 1, illustrating in longitudinalcross-section a multi fluid injection mixer 7 according to the presentinvention, which injection mixer includes a contacting element (2, 2 a,2 b) formed as an inverse cone ring, i.e. the cross-section of thecontacting element, along the radius of the ring, is an inverse cone.The inlet pipe 1 conducts fluid to be processed to the mixer. Thecontacting element 2, formed as an inverse cone ring with inner 2 b andouter 2 a contacting surfaces, accelerates the fluids of the pipecontinuously towards a prescribed maximum velocity and dynamic pressure.The diameter of the outlet of the contacting surfaces is determined bythe dynamic pressure/drag force required to tear off the injected fluidsefficiently at a sharp edge (4, 4 a, 4 b) at the outlet. The injectionelements 3 a and 3 b are used for injection of admixture fluids to forma liquid/gas bubble film on the inner contacting surfaces. The injectionelements include a chamber or ring conduit from which the injectedfluids are guided to the contacting surfaces via a continuous channel.The diameter and length (depth) of the channel, both preferablyadjustable, are calculated by the liquid/gas fluid properties andliquid/gas admixture injection flow rate so that the pressure drop overthe circular channel normally exceeds the difference in gravity headover the periphery for a horizontally mounted mixer. At the downstreamend of the contacting element the sharp edges 4 a and 4 b are situated,one for each contacting surface, preferably sharp edges having anglelower than 90°, designed so that the liquid/gas bubble film isaccelerated by the drag exerted by the fluid contents and is torn intoliquid/gas bubble filaments in the downstream volume rather than“creeping” at the pipe wall to the downstream side. An expanding element5, formed as a diverging pipe, is arranged downstream to the contactingelement and sharp edge, for deceleration towards the normal pipe flowvelocity. The angle and length of the expanding element is particularlyimportant for the turbulence generation and permanent pressure drop overthe injection mixer. The outlet pipe 6 guides the processed fluidmixture further. As illustrated in the figure by the size anddistribution of the droplets/bubbles in the outlet pipe 6, droplets andgas bubbles are broken up into extremely small sizes and distributedvery uniformly over the foil cross-section of the pipe. The size of thedroplets/bubbles can be as small as a few microns.

The embodiment illustrated in FIG. 1, formed as a inverse cone ring,includes two contacting surfaces, namely one on each side of the inversecone, with one injection element for admixture injection for eachcontacting surface. The sharp edges are located at 4 a and 4 b,respectively, formed as sharp edge rings. FIG. 2 illustrates the multifluid injection mixer of FIG. 1, as viewed from below, i.e. from thedownstream side. The sharp edges 4 a and 4 b are indicated. Theembodiment illustrated on FIGS. 1 and 2 is very favorable with respectto mixing and deposition, which means that the injected admixture fluidsare very uniformly mixed for a long section downstream without beingdeposited on the internal pipe wall.

Many alternative geometries are possible, of which a few preferable onesare illustrated.

FIG. 3 illustrates a multi fluid injection mixer called C700, with 7cone section formed contacting elements. Said injection mixer provides alarge contacting surface area and a large length of sharp edge, i.e.slip edge, relative to the cross-section of the pipe. Further, threepipe fluid bypass openings 10 along the internal pipe wall are provided,resulting in a pipe fluid “curtain” along the internal pipe wall,decreasing the admixture deposition on the internal pipe wall. Thereforethe technical effect is favorable.

A different embodiment can be seen on FIG. 4, which illustrates aninverse cone mixer, where the inverse cone is located coaxial to thepipe axis. The volume of turbulence is located downstream and leeward ofthe inverse cone, which means away from the internal pipe wall,resulting in a low deposition rate of the injected admixture fluids.

FIG. 5 illustrates an embodiment of the multi fluid injection mixture ofthe present invention, designated a ring mixer, which mixer is anembodiment of the inverse cone ring mixer illustrated on FIGS. 1 and 2,providing a quite similar technical effect. The deflection of the pipefluid flow increases close to the sharp edge, which can be beneficial.

The contacting element could alternatively be formed as a flange with atleast one opening, preferably one opening coaxial with the pipe flow, oran internal gutter around the periphery of the pipe. With a contactingelement formed as a cone section the injected fluids or admixtures flowco-currently with the fluid of the pipe. With a contacting elementformed as flange or similarly the injected fluids flow laterally orcross-currently to the general direction of flow through the pipe. Witha contacting element formed as a gutter, the injected fluid flows atleast partly countercurrently to the main flow direction of the pipe.The contacting element embodiments resulting in at least partial crosscurrent flow or counter current flow of the injected admixture fluidswill have a more stagnant area on the surface nearest the pipe wall, inwhich more stagnant area a thicker film of injected liquids/gas bubblescan be accumulated for being entrained by slugs or increased flow rates.Also the orientation of the conduit relative to the direction of themain flow or the surface area towards the multiphase pipe flow willaffect the local boundary condition in terms of the pressure at theoutlet of the admixture fluid conduit. Thus when the flow momentum ofthe multiphase flow is increased, the suction as caused by increaseddynamic pressure will serve to increase the flow rate of the admixturefluid to some proportion. Thus, a sort of self regulating is achieved,which can be beneficial for fluctuating pipe flow conditions. Further,the degree of constriction can be different.

As a further explanation and with reference to FIG. 1, without wishingto be bound by theory, the droplet generation sequence can be dividedinto four stages, of which A designates that initially an annular filmof the injected fluid is exposed to accelerating pipe fluid flow. At B,the special sharp edge geometry favors the generation of filaments ofthe injected fluids into the continuous flow. At C, the filaments of theinjected fluid are broken up into small droplets. The breaking up isdetermined by the Weber number (We-number) as calculated from thesurface tension σ between the pipe fluid phase and the injected fluid,the characteristic filament dimension d, the relative velocity U and thedensity ρ of the continuous phase (ref. Krzeczkowski, 1980):We=ρ ^(·) U ^(2·) d/σ

Break-up corresponds to We>We_(er). For wind tunnel experiments anddroplet injection into the flow field. We_(er) has been determined to be8-10. At D radial droplet mixing takes place, determined by the initialbreak-up of the filament droplets and the local turbulence, asrepresented by the local Reynolds number of the pipe flow.

It is important to control the injection pressure and injection ratesuch that admixture fluids are injected onto the internal contactingsurfaces rather than into the pipe flow, and such that pipe fluids donot flow into the injection equipment.

Reference is made to FIG. 6 that is an illustration of an assemblyaccording to the present invention. More specifically the assemblycomprises the multi fluid injection mixer 7 of the invention arrangedwith a pipe section 8 and a re-mixer 9. The re-mixer is in accordance todescription of patent publication U.S. Pat. No. 5,971,604. Morespecifically, the re-mixer comprises a housing to be inserted in thepipe for the fluid to flow through, and in the housing there are atleast one and preferably two or more adjoining and individuallydisplaceable sealingly arranged regulating elements having cooperatingwall portions with flow passages. The regulating elements can beadjusted for the flow passages to be focused at one point in a centralchamber, or to be misaligned, with respect to inlet passages and outletpassages from the central chamber, thereby controlling the flow andmixing action. For further details, please refer to U.S. Pat. No.5,971,604. The assembly is particularly useful for processing ofproduced water, to reduce the contamination of oil.

EXAMPLE 1 Treatment of Produced Water

An assembly according to FIG. 6 was used to reduce the contents of oilin produced water. The injection mixer had an injection element formedas a cone section. The re-mixer was according to claim 2 of U.S. Pat.No. 5,971,604. Two admixture fluids were injected, namely nitrogen gasupstream of a liquid flocculant. Nitrogen can be replaced partially orcompletely by natural gas. The pipe length was in the range 0.1-30 m.The actual volumetric flow rates were in general as follows:

-   -   Produced water: Q_(w)    -   Nitrogen gas: Q_(w) ^(·)10⁻²    -   Flocculant: Q_(w) ^(·)10⁻⁵

With corresponding flow rates an equally good or better performance canbe achieved with respect to oil contents in the downstream separatedproduced water compared to an injection arrangement of two C100injection mixers in series, at 50% of the pressure drop, or comparedwith an injection arrangement of flocculant injected in a quill ornozzle upstream a C100 injection mixer used for gas injection. Thepressure drop was in the range 0.02-2 bar depending on the pipe flowconditions. The injected gas provided a flotation effect. The re-mixermaintained the flotation effect of the gas bubbles and the uniformdistribution of the flocculent and gas bubbles over the full crosssection of the pipe.

A distance downstream of the re-mixer equipment for separation of oilfrom water is installed, for example a hydrocyclone, which has proved tobe efficient for the separation of oil from water flow including gasbubbles and coalesced oil droplets. The re-mixer is adjustable withrespect to mixing action and can be operated such that operation ofdownstream separation equipment is efficient, even at somewhat varyingpipe flow rate, as far as the variations can be compensated for byregulating the mixing action of the re-mixer. The re-mixer can bereplaced by a mixer according to the invention or an injection mixer ofthe invention or the C100 injection mixer, the injection mixers withoutinjection of further chemicals but merely operating as a mixer, oralternatively with further injection of admixtures. However, theassembly of the invention, with the injection mixer and re-mixerconnected via a pipe section, provides a technical effect for treatmentof produced water as yet unknown. It is assumed, without wishing to bebound by theory, that the injection mixer arrangement with the conduitof gas followed by the conduit of flocculant serves to change thevelocity profile and the wall shear stress exposed to the injectedflocculant. The gas is immediately dispersed into small bubbles andlocally increase the flow velocity of the multiphase flow in thevinciniry of the wall of the injection part of the mixer. This serves toincrease the velocity gradient and hence also the shear stress asimposed to the injected flocculant. As result an efficient homogeneousdispersion of the flocculant is generated. This is particularlyimportant if the residence time of the flocculant prior to separation islimited.

EXAMPLE 2 Treatment of Oil

This example relates to use of the assembly of the invention in a methodfor treatment of oil. Conventional oil-water treating is normallycarried out in large horizontal vessels to allow for gravity settling ofthe water droplets. In the treatment of heavy oil systems it is normallyrequired to apply considerable amounts of demulsifying chemical toeffectively disengage water from oil to meet required productspecification of less than 0.5% BS&W volume fraction Basic Sediment andWater). The demulsifier is a surface active compound that competes withthe natural surfactants in the oil to displace them from the oil-waterinterface. Thus the interfacial film around droplets can be disrupted tofacilitate droplet-droplet coalescence.

With the use of prior art equipment such as injection nozzles andinjection quills, it is very difficult to make sure that thedemulsifying agent arrives at the droplet surfaces that are dispersed inthe continuous oil stream. Thus overdosing of chemical can become aproblem—instead of destabilizing an emulsion, a new emulsion can beformed, resulting in malfunction of the oil-water separator.

It is known that recirculation of produced water can enhance separatorperformance due to increase in critical water cut and the possible phaseinversion to a water continuous system. Using the dual injectionfunction of the injection mixer, the recirculated produced water anddemulsifying agent can be injected upstream of the production separator.Once water with demulsifying agent is injected and mixed homogeneouslyin the continuous phase, the re-mixer according to U.S. Pat. No.5,971,604, is used to create new surface area for droplet-dropletcoalescence. With careful re-mixing of the injected chemical,recirculated water and the multiphase flow to be treated, thedemulsifying chemical can reach the new surface area of the droplets andimmediate and effective water droplet coalescence can commence. In factsuch effective mixing of demulsifying agent and following coalescence ofwater droplets can reduce the water content in the oil with at least 35%in comparison with conventional systems. Alternatively, 20% lessdemulsifying chemical can be applied to the process and still yield thespecification of 0.5% BS&W.

EXAMPLE 3 Desalting

This example relates to use of the assembly of the invention in a methodfor desalting crude oil. Crude oil often contains water, inorganicsalts, suspended solids, and water-soluble trace metals. As a first stepin the refining process, to reduce corrosion, plugging, and fouling ofequipment and to prevent poisoning the catalysts in processing units,these contaminants must be removed by means of desalting, comprisingadmixture injection, including water, multiphase flow mixing anddownstream separation.

The two most typical methods of crude-oil desalting, based on chemicaland electrostatic separation, use hot water as the extraction agent. Inchemical desalting, water and chemical surfactant (demulsifiers) areadded to the crude, heated so that salts and other impurities dissolveinto the water or attach to the water, and are then routed into a tankwhere they settle out. Electrical desalting is the application ofhigh-voltage electrostatic charges to concentrate suspended waterdroplets in the bottom of the settling tank. Practical processimplementation for desalting might also include the combination of thesemethodologies.

Prior art equipment for the injection/mixing of injection ofwater/demulsifying agent can be the combination of injection quill withdownstream Sulzer mixer or choke valve.

The use of the assembly of the invention will safeguard the effectiveand homogeneous distribution of warm water and demulsifier such thatoptimum surface area is created for the salt to be extracted from theoil into the injected water. In can be expected that efficiency for theprocess will be improved both in terms of amount of demulsifiernecessary for achieving a specified quality, the pressure drop requiredfor the process and the volumetric handling capacity of the desaltingprocess.

EXAMPLE 4 Flow Assurance

This example relates to use of the assembly of the invention in a methodfor flow assurance. Flow Assurance includes all issues important tomaintaining the flow of oil & gas from the reservoir to the receptionfacilities. Potential pipeline blockage issues can be related tohydrates, wax, asphaltenes, scale or sand.

The formation of hydrates is a major operational and safety problemwhich can occur unpredictably in subsea pipelines and well headfacilities. Gas hydrates can potentially be formed in subsea flowlinesunless the water content is removed to below the lowest dew pointencountered. Typically precautions are pipeline insulation, heatingand/or inhibitors. The conventional approach to inhibition of hydratesis the injection of methanol or glycol in the pipeline. In this way thehydrate formation occurrence line is shifted towards lower temperaturesfor the pressure level in concern.

With use of the assembly of the invention, methanol together with airreversible reacting triazine chemical is injected in the pipeline tosimultaneously remove highly corrosive H₂S and to prevent the formationof hydrates. The triazine based chemical forming more stable film orfilaments is injected through the injection element of the multipleinjection mixer closest to the sharp edge whereas the methanol or glycolis injected through the injection element most remote from the sharpedge. By this also the velocity profile of the pipe flow is affectedsuch that the shear stress at the surface area towards the sharp edge isincreased. As a consequence a more efficient deformation of thefilaments and generation of secondary droplet break-up of triazineresults as compared to no immediate injection of methanol upstream theinjection of triazine.

EXAMPLE 5 Comparisons with C100

Surprisingly, the preferred embodiments of the multi fluid injectionmixers of the present invention utilize the turbulence generated by thesharp slip edge to distribute and maintain the droplets in a gas phase,and probably similar for any pipe fluid phase, for a longer time thanthe C100. By changing the geometry which defines the contacting elementand slip edge, the turbulence surprisingly helps to keep the droplets inthe gas phase. The new geometries allow the gas to flow over the sharpslip edge, as well as generating a gas curtain between the wall and thesharp slip edges. This serves to reduce the droplet deposition rate ascompared to the C100.

FIG. 7 and FIG. 8 show some typical parameters where three embodimentsof the invention are compared with the C100 mixer.

FIG. 7 shows the fraction of the total liquid flux (admixture fluid)flowing with the gas phase (pipe fluid) at the position 40 cm after theinjection point. The rest of the liquid is flowing as liquid film on thepipe wall. As can be seen from the table, significant improvement hasbeen achieved with the present invention in terms of entrainmentfraction at the downstream position.

FIG. 8 shows the pressure drop recorded when the mixer was tested withair at 1 bara and a superficial velocity of 22 m/s. The table also showsthe G-factor which characterizes the geometry in an aerodynamic point ofview. It is advantageous to have G as low as possible as this representsa potential for low permanent pressure drop over the mixer unit.

The tested embodiments are illustrated on the drawings as follows:

FIG. 3 illustrates an injection mixer C700, with 7 cones (contactingelements) and 3 passageways for fluid along the pipewall (pipe fluidbypass openings 10),

FIG. 4 illustrates an inverse cone mixer, and

FIG. 5 (and FIGS. 1 and 2 also) illustrates an inverse cone ring mixer,which mixer sometimes is called a ring mixer.

The multi fluid injection mixer, the mixer and the assembly according tothe present invention can in principle be used in any industry wheremixing, injection and fluid conditioning can be undertaken in a pipecontaining flowing fluids.

The invention claimed is:
 1. An injection mixer for injecting andhomogeneously mixing at least one injected fluid with a pipe fluid, theinjection mixer extending between an inlet and an outlet, eachconfigured to be coupled to a pipe, and comprising at least onecontacting element, each contacting element(s): having one or morecontacting surfaces, that each: extends between a first end of thecontacting element and a second end of the contacting element, an edgebeing defined at the second end of the contacting element; defines amixing channel through the contacting element; and converges such thatthe cross-sectional area of the mixing channel decreases from the firstend of the contacting element to the second end of the contactingelement to define a minimum cross-sectional flow area of the mixer atthe second end; and defining at least one injection path through aportion of the contacting element to and through at least one of thecontacting surface(s) such that, when the pipe fluid flows in the mixingchannel from the first end to the second end, the injection path isconfigured to inject admixture fluid onto the contacting surface suchthat the pipe fluid entrains the admixture fluid along the contactingsurface and over the edge; where at least one of the injection path(s)is configured to inject a first admixture fluid that comprises a hydrateinhibitor; and where the first end of each contacting element faces theinlet of the mixer.
 2. The injection mixer of claim 1, the injectionmixer situated within a pipe configured to conduct pipe fluid subsea andwherein the first end is upstream of the second end.
 3. The injectionmixer of claim 2, wherein for at least one of the contacting element(s),the at least one injection path comprises at least a first and secondinjection path, the first injection path configured to inject the firstadmixture fluid and the second injection path configured to inject asecond admixture fluid.
 4. The injection mixer of claim 3, wherein, forat least one of the contacting surface(s), the first injection path isconfigured to inject the first admixture fluid onto the contactingsurface at a first location and the second injection path is configuredto inject the second admixture fluid onto the contacting surface at asecond location that is closer to the second end than is the firstlocation.
 5. The injection mixer of claim 2, wherein each of thecontacting element(s) comprises a conical ring such that the mixingchannel(s) comprise: an outer mixing channel comprising a frustoconicalannulus having a central axis coaxial with a central axis of the pipeand a first cross-section that is disposed at the first end and a secondcross-section that is disposed at the second end and is larger than thefirst-cross section; and a frustoconical inner mixing channel having acentral axis coaxial with the central axis of the pipe.
 6. The injectionmixer of claim 2, wherein the contacting element(s) comprise a pluralityof contacting elements positioned over the cross-section of the pipe,wherein for each of the contacting elements the mixing channel(s)comprise a frustoconical mixing channel.
 7. The injection mixer of claim2, wherein for at least one of the contacting element(s), at least oneof the contacting surface(s) forms a cone having a central axis coaxialwith a central axis of the pipe and a first cross-section that is at thefirst end and a second cross-section that is at the second end and issmaller than the first cross-section such that the mixing channelcomprises a frustoconical annulus.
 8. A method of using the injectionmixer of claim 2, comprising, for each of the mixing channel(s) of eachof the contacting element(s): communicating the pipe fluid through themixing channel from the first end to the second end; and injecting afirst admixture fluid comprising a hydrate inhibitor through a firstinjection path of the at least one injection path such that the firstadmixture fluid flows onto the contacting surface and is entrained bythe pipe fluid.
 9. The method of claim 8, further comprising, for eachof the mixing channel(s) of each of the contacting element(s), injectinga second admixture fluid through a second injection path of the at leastone injection path such that the second admixture fluid flows onto thecontacting surface and is entrained by the pipe fluid.
 10. The method ofclaim 9, where the second admixture fluid comprises at least one of acorrosion inhibitor, a scale inhibitor, and a wax inhibitor.
 11. Themethod of claim 9, wherein the first admixture fluid is glycol ormethanol and the second admixture fluid is triazine.
 12. The method ofclaim 8, wherein the injecting comprises adjusting an aperture of thefirst injection path, thereby adjusting the flow rate of the firstadmixture fluid.
 13. The method of claim 9, wherein the injecting isperformed such that the first admixture fluid is injected onto thecontacting surface at a first location and the second admixture fluid isinjected onto the contacting surface at a second location that is closerto the second end than is the first location.